10 March 2013

"Year of Macrauchenia": Third and Final "All Your Yesterdays" Entry

Macrauchenia was the greatest and last of the litopterns, a clade of stem-euungulates. This bizarre Pleistocene South American herbivore is often described as having the body of a llama and the head of a tapir. However, the body is only superficially llama-like (but with gigantic elbows) and the head is not at all tapir-like. (If any part of it resembles tapirs, it's the feet.) In fact, the skull isn't like that of any living terrestrial mammal. It has extremely dorsal nares, like trunked animals and cetaceans, but it lacks any place for trunk muscles to attach.

But there is a possible analogue— another group of terrestrial herbivores with extremely dorsal nares — and they even had long necks, too! I refer, of course, to sauropod dinosaurs. Unfortunately, none are extant for comparison, but recent work has shown that, despite the dorsal placement of the nares in the skull, the external nostrils were still placed rostrally, close to the mouth, thanks to fleshy tubes. I've restored Macrauchenia similarly.

This mandala depicts the life of Macrauchenia across the seasons. At bottom, a lone Macrauchenia wanders the frozen highlands in relative comfort, having grown a shaggy winter coat. Its fleshy nostril tubes serve to warm the air before it enters the body. At right, spring is in effect — a bull courts a cow by inflating his nostril tubes, similar to a hooded seal. At top, a young calf frolics under his mother's watchful eye—his green color comes from the algae living in his fur (similar to the camouflage of those other South American indigenes, the sloths). This extra measure of color accuracy is necessary because, unlike today's ungulates, Macrauchenia must contend with predators that have excellent color vision: phorusrhacids. At left, a wary bull faces off against a Smilodon, an invading predator from the north. (It is restored after linsangs, the extant sister group to felids, instead of the felids themselves, since it is, properly, a stem-felid, not a true felid.) Macrauchenia will survive this great faunal interchange, but not for long — another invader from the north, a large primate, will be the end of it, and hence all litopterns.